[2] _Principles of Biology_, Sec. 166, footnote. The English jaws are
somewhat lighter than the Australian jaws, though I could not undertake
to affirm that they are really shorter and smaller. In the typical
skulls depicted on p. 68 of the official guide to the mammalian
galleries at South Kensington, the typical Caucasian jaw is very much
larger than the Tasmanian jaw, although the repulsively obtrusive teeth
of the latter convey the contrary idea to the imagination. Mr. Spencer's
assumption that the ancient Britons had large jaws appears to me
erroneous. (See Professor Rolleston's _Scientific Papers and Addresses_,
i. p. 250.)
[3] Romanes, Galton, and Weismann have made great use of this principle
in explaining the diminution of disused organs. Weismann has given it
the name of _Panmixia_,--_all_ individuals being equally free to survive
and commingle their variations, and not merely selected or favoured
individuals. See his _Essays on Heredity_, &c., p. 90 (Clarendon Press).
[4] Inclusive in each case of fixed strengthening wire weighing about a
sixteenth of an ounce or less.
[5] References of course are to _Factors of Organic Evolution_.
[6] P. 13; and _Nineteenth Century_, February, 1888, p. 211.
[7] Tomes's _Dental Surgery_, pp. 273-275. Tomes observes that it is as
yet uncertain in what way civilization predisposes to caries. But he
shows that caries is caused by the lime salts in the teeth being
attacked by _acids_ from decomposing food in crevices, from artificial
drink such as cyder, from sugar, from medicine, and from vitiated
secretions of the mouth. It is evident that in civilized races natural
selection cannot so rigorously insist on sound teeth, sound
constitutions, and _protective alkaline_ saliva. The reaction of the
civilized mouth is often acid, especially when the system is disordered
by dyspepsia or other diseases or forms of ill-health common under
civilization. The main supply of saliva, which is poured from the cheeks
opposite the upper molars, is often acid when in small quantities. But
the submaxillary and sub-lingual saliva poured out at the foot of the
lower incisors and held in the front part of the jaw as in a spoon,
"differs from parotid saliva in being more alkaline" (Foster's _Text
Book of Physiology_, p. 238; Tomes, pp. 284, 685). One observer says
that the reaction near the lower incisors is "never acid." Hence (I
conclude) the remarkable immunity of the lower incisors and canines from
decay, an immunity which extends backwards in a lessening degree to the
first and second bicuspids. The close packing of the lower incisors may
assist by preventing the retention of decaying fragments of food. Sexual
selection may promote caries by favouring white teeth, which are more
prone to decay than yellow ones. Acid vitiation of the mucus might
account both for caries and (possibly) for the strange infertility of
some inferior races under civilization.
[8] _Origin of Species_, pp. 198-9; _Variation of Animals and Plants
under Domestication_, vol. ii. p. 328 footnote, also p. 206.
[9] Mr. Spencer weakly argues that an advantageous attribute (such as
swiftness, keen sight, courage, sagacity, strength, &c.) cannot be
increased by natural selection unless it is "of greater importance, for
the time being, than most of the other attributes"; and that natural
selection cannot develop any one superiority when animals are equally
preserved by "other superiorities." But as natural selection will
simultaneously eliminate tendencies to slowness, blindness, deafness,
stupidity, &c., it _must_ favour and improve many points simultaneously,
although no one of them may be of greater importance than the rest. Of
course the more complicated the evolution the slower it will be; but
time is plentiful, and the amount of elimination is correspondingly
vast.
[10] I venture to coin this concise term to signify _the direct
inheritance of the effects of use and disuse in kind_. Having a name for
a thing is highly convenient; it facilitates clearness and accuracy in
reasoning, and in this particular inquiry it may save some confusion of
thought from double or incomplete meanings in the shortened phrases
which would otherwise have to be employed to indicate this great but
nameless factor of evolution.
[11] _Origin of Species_, pp. 230-232; Bates's _Naturalist on the
Amazons_. Darwin is "surprised that no one has hitherto advanced the
demonstrative case of neuter insects, against the well-known doctrine of
inherited habit, as advanced by Lamarck." As he justly observes, "it
proves that with animals, as with plants, any amount of modification may
be effected by the accumulation of numerous, slight, spontaneous
variations, which are in any way profitable, without exercise or habit
having been brought into play. For peculiar habits confined to the
workers or sterile females, however long they might be followed, could
not possibly affect the males and fertile females, which alone leave any
descendants." Some slight modification of these remarks, however, may
possibly be needed to meet the case of "factitious queens," who
(probably through eating particles of the royal food) become capable of
producing a few male eggs.
[12] _Descent of Man_, pp. 573, 572, and footnote.
[13] _Contemporary Review_, December, 1875, p. 92.
[14] See _Origin of Species_, pp. 5-8. "Changed conditions induce an
almost indefinite amount of fluctuating variability, by which the whole
organization is rendered in some degree plastic" (_Descent of Man_, p.
30). It also appears that "the nature of the conditions is of
subordinate importance in comparison with the nature of the organism in
determining each particular form of variation;--perhaps of not more
importance than the nature of the spark, by which a mass of combustible
matter is ignited, has in determining the nature of the flames" (_Origin
of Species_, p. 8).